The present invention relates generally to a method and an apparatus for power allocation used by a BTS (base transceiver station) in a mobile telephone system, and more particularly to a method and an apparatus wherein an available radio power is distributed between a plurality of carriers.
Cellular radio is a technique that provides mobile telephony by using the allotted radio band in an efficient manner. Cellular telephone service involves the subdivision of a service area into a number of smaller cells to facilitate frequency-reuse and an increasing number of users. In these new cellular systems micro computer based switches can follow a moving object by way of power and signal quality measurements from the numerous antennas that constitute the cellular system and order the mobile object to change the frequency according to the cell of the object. Each cell requires a BTS (base transceiver station) and an antenna operating in a frequency-band with a power output just sufficient to cover the area of the cell. The BTS:s are connected to a BSC (Base Station Controller) which performs the switching function as well as the tracking of the users. When the user with the mobile telephone moves from one cell to another the BSC must, owing to signal quality or to achieve load sharing among different antennas by peaks in the traffic, hand over an ongoing call from the original antenna to another more suitable antenna. Cellular systems are based on both analogue and digital transmission. Digital cellular systems provide the best quality with the least amount of bandwidth. Different kinds of principles are used for digital cellular systems. One of these is the TDMA-principle (Time Division Multiple Access), which transmission is in the form of a repetitive sequence of frames, each of which is divided into a number of slots. All the users sharing the physical resource are dedicated to a particular time slot within a group of time slots.
Another principle for cellular systems is the CDMA-technology (Code Division Multiple Access). This is probably the next generation of digital cellular systems.
A cellular system or cellular network comprises various subsystems, devices and equipment. A base transceiver station (BTS) or a base station (BS) is one of the most important subsystems in a cellular network, which base station is the mobile interface to the network. The base station doesn't have to be located in the centre of a cell, but the antenna usually is. The cell size is limited by the determined transmitting power of the base station. Further, a base station may have several transceivers, each of which represents a separate RF (Radio Frequency) channel. A state of the art radio frequency power amplifier is designed to handle one carrier at a time, independent of the other carriers.
In sites used for mobile telephony, the maximum radio power available for each carrier is determined considering each particular cell radius.
Cells are planned for different coverage, and, therefore, BTS:s have to be provided with transceivers of various performance.